From: "charles.99@sky.com" <charles.99@sky.com>
To: 'Microcontroller discussion list - Public.' <piclist@mit.edu>
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Date: Wed, 14 Jul 2021 03:45:36 -0700
Subject: RE: [EE] Redundant PSU for critical NAS server
Thread-Topic: [EE] Redundant PSU for critical NAS server
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I'm no expert, but if the 2 supplies are adjustable, I'd set it so each sup=
ply gave around 50% of the load.

As both are under run, reliability should be improved.

If one fails the other assumes 100% of the load, but that would happen anyw=
ay in your scheme.

Just a thought,

Charles


-----Original Message-----
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> On Behalf Of foros@=
arocholl.com
Sent: 12 July 2021 15:13
To: piclist@mit.edu
Subject: [EE] Redundant PSU for critical NAS server

Hi there,

Over the last couple of years have experienced problems with PSU failing an=
d shutting down connected NAS servers, twice. These PSUs are 12v/100W exter=
nal units from the manufacturer (Synology). The funniest thing is the PSUs =
are fully protected with 220v UPS but of course nothing helps if they fail =
themselves, and they do, without any advice... Not a good setup for a criti=
cal server.

So I rather no longer rely on the manufacturer PSU and design my own, overr=
ated 12v/200W redundant supply. My current thinking is to proceed like this=
:

* Have two identical 12v PSU adjusted to different DC levels (12.6v and
12.2v) each one connected to a pair of schottky diodes (2x parallel 15V 9A =
95SQ015 I have spare) so one PSU is the active one and the second PSU is ru=
nning ready but passive.
* In theory if the active PSU fails, the passive one becomes active and dio=
des prevent anything funny from happening.

[Active PSU 12.6v]  -> 2x Parallel Diode -> Joint [Passive PSU 12.2v] -> 2x=
 Parallel Diode -> Joint -> NAS server

I've been testing this setup and the diodes get barely warm so everything l=
ooks kosher to move to production. I also tested the active/passive -> dead=
/active scenario with some alternative charge but don't want to risk the ac=
tual server with a full charge test.

So I wanted to check if you have been there already and found a better setu=
p, or if this approach may have an obvious issue I currently do not see.


Regards,
Ariel
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